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#! /usr/local/bin/guile -s
!#
;;; Commentary:
;;; This is a command-line factorial calculator. Run like this:
;;;
;;; ./fact 5
;;;
;;; to calculate the factorial of 5
;;; Author: Martin Grabmueller
;;; Date: 2001-05-29
;;; Code:
(use-modules (ice-9 getopt-long))
;; This is the grammar for the command line synopsis we expect.
;;
(define command-synopsis
'((version (single-char #\v) (value #f))
(help (single-char #\h) (value #f))))
;; Display version information and exit.
;;
(define (display-version)
(display "fact 0.0.1\n"))
;; Display the usage help message and exit.
;;
(define (display-help)
(display "Usage: fact [options...] number\n")
(display " --help, -h Show this usage information\n")
(display " --version, -v Show version information\n"))
;; Interpret options, if --help or --version was given, print out the
;; requested information and exit. Otherwise, calculate the factorial
;; of the argument.
;;
(define (main options)
(let ((help-wanted (option-ref options 'help #f))
(version-wanted (option-ref options 'version #f))
(args (option-ref options '() '())))
(cond
((or version-wanted help-wanted)
(if version-wanted
(display-version))
(if help-wanted
(display-help)))
((not (= (length args) 1))
(display-help))
(else
(display (fact (string->number (car args))))
(newline)))))
;; Calculate the factorial of n.
;;
(define (fact n)
(if (< n 2)
1
(* n (fact (- n 1)))))
;; Call the main program with parsed command line options.
;;
(main (getopt-long (command-line) command-synopsis))
;; Local variables:
;; mode: scheme
;; End:
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